The present invention relates to multicouplers and methods for increasing the range of receivers in radio communication systems, and more particularly to a multicoupler and method for a cellular/PCS communication system in which antenna-tower mounted multicoupler components are cooled to reduce noise, thereby increasing base station range.
As is known, the performance of some electronic components improves as the temperature of the device decreases. For example, materials that exhibit greatly improved performance at less than about 77.degree. K. are known as superconductors. Superconductor materials only exhibit their "zero resistance" when operated below a critical temperature. The use of such materials in radio systems is known, although the use is limited due to the complexity and cost of maintaining the proper device temperature. See, for example, the selective filter system in U.S. Pat. No. 5,244,869 issued to Billing Sep. 14, 1993 in which improved performance is achieved by using various types of superconductor materials that operate at low superconductor temperatures (e.g., 4.degree. K.) or high superconductor temperatures (e.g., 70.degree.-75.degree. K.).
Cooling to about 150.degree. K. provides many of the benefits of superconductivity, and recent developments in cooling technology have made this temperature achievable in a relatively small closed-system unit. For example, a cascade mixed gas throttle expansion cycle refrigeration unit is discussed in "Development of a Low Cost, Cryogenic Refrigeration System for Cooling of Cryoelectronics", W.A. Little and I. Sapozhnikov (MMR Technologies, Inc., Mountain View Calif).
Some radio components, such as amplifiers, that are already low noise amplifiers may have their noise further reduced by cooling. However, low noise amplifiers typically exhibit less than desirable dynamic range, or linearity, for many radio applications, such as cellular/PCS systems that are susceptible to distortion from a multiplicity of high powered signals. Cellular/PCS systems typically operate at 1800-1900 MHz where signal propagation losses are higher than in other cellular systems that operate at 800 MHz. High dynamic range, or highly linear, amplifiers that are used for receivers in cellular/PCS systems do not demonstrate low noise performance, and it is desirable that they do so. While the use of superconductor materials may provide improved performance for cellular/PCS systems, the cost of installing superconductor materials and cooling systems in amplifiers of the receivers at each site in a cellular/PCS system, if it could be done at all, would far outweigh the cost benefits of any improvement.
Nevertheless, it is desirable to increase the sensitivity of receivers in cellular/PCS systems (i.e., extend their range) to thereby reduce the number of sites for the receivers. The present invention finds application in receivers in cellular/PCS systems and in other radio systems where the improvements available from the invention may be beneficial.
Accordingly, it is an object of the present invention to provide a novel method and multicoupler for a receiver at a base station in a radio communication system that obviates the problems of the prior art.
It is another object of the present invention to provide a novel method and multicoupler for a receiver in which a container for a highly linear amplifier is cooled to between 100.degree. K. and 175.degree. K. and mounted on an antenna tower adjacent an antenna for reducing amplifier noise and thereby increasing receiver range.
It is yet another object of the present invention to provide a novel method and multicoupler for a receiver in which a preselector filter, a highly linear amplifier, a directional coupler, and the connections therebetween are in a container that is cooled to about 150.degree. K. and mounted on an antenna tower.
It is still another object of the present invention to provide a novel method and multicoupler for a cellular/PCS receiver in which subscriber handset power may be reduced and building penetration improved due to improved base station sensitivity achieved through cooling a multicoupler amplifier and mounting the cooler amplifier on an antenna tower adjacent an antenna.
It is a further object of the present invention to provide a novel method and multicoupler for a receiver in which a container for a highly linear amplifier is cooled to between 100.degree. K. and 175.degree. K. and mounted on an antenna tower adjacent an antenna for reducing amplifier noise and required gain, and in which a second amplifier at a ground station increases received signal gain without significantly increasing noise.
It is yet a further object of the present invention to provide a novel method and multicoupler for a receiver in which a preselector filter, and a highly linear amplifier are in a container that is cooled to between 100.degree. K. and 175.degree. K., where the filter is a cavity filter with plural sections.
It is still a further object of the present invention to provide a novel method and multicoupler for a receiver in which a preselector filter, and a highly linear amplifier are in a container that is cooled to between 100.degree. K. and 175.degree. K. by a closed-system cooler with a selector for setting a specific temperature within the range.
It is an additional object of the present invention to provide a novel method and multicoupler for a duplex antenna channel in which a transmit filter, a receive filter and an amplifier are cooled in a container located adjacent an antenna on a tower so that power dissipated by the transmit filter is reduced.
These and many other objects and advantages of the present invention will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.